1. Field of the Invention
The present invention relates to a chain tensioner device having a main arm pivotably supported by a first support shaft and brought into slide contact with an endless chain to apply a predetermined tension to the endless chain. The endless chain is wrapped around a drive sprocket provided on a driving shaft and a follower sprocket provided on a follower shaft. A tensioner lifter generates a biasing force to bias the main arm toward the endless chain. A sub-arm is pivotably supported by a second support shaft and transfers the biasing force of the tensioner lifter to the main arm.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2004-100886 discloses a device having a flexible tensioner arm that abuts against a loose side of a timing chain which transfers rotation of a crankshaft of an engine to a camshaft. The device further has a control arm provided between a plunger of a hydraulic tensioner lifter and the tensioner arm. The control arm prevents any oscillation of the flexible tensioner arm from being transmitted to the tensioner lifter to increase extension and contraction response as well as improve the durability of the tensioner lifter.
The plunger is configured to be biased in a protruding direction by hydraulic pressure and a biasing force of a spring. When biased, the plunger extends and presses the tensioner arm against the timing chain, and then receives a reaction force from the timing chain that causes the plunger to retract in a direction opposite to the protruding direction. Thus, there is a problem wherein an increase in the plunger stroke reduces extension and contraction response, and wherein the extension and contraction of the plunger cannot follow or correspond to changes in the tension of the timing chain during short intervals. To increase the extension and contraction response of the plunger, the stroke of the plunger needs to be reduced, but reducing the stroke of the plunger more than necessary is undesirable for ensuring a required stroke of the tensioner arm.